A storage system configured with a plurality of disks as a redundant array of independent disks (RAID) to ensure availability and reliability are known. In case of a failure of disks included in a RAID, shared spare disks may be prepared for a plurality of RAID groups in the storage system or spare disks dedicated to a specific RAID group may be prepared. When a disk failure occurs, the storage system conducts recovery from the failure through a rebuild process involving a spare disk.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication No. 2009-187406 and Japanese Laid-open Patent Publication No. 2005-100259.
However, a storage system may manage a multitude of disks as a disk pool by providing a plurality of storage units called disk boxes or disk enclosures that are able to accommodate a certain number of disks.
While this type of storage system configures a RAID with each disk in a different storage unit to address reliability, when a rebuild process involving a spare disk is conducted due to a disk failure, a plurality of disks included in the RAID may contained in the same storage unit. In this case, when a failure occurs at the storage unit level, the storage system may suffer from data loss due to the failure of the plurality of disks at the same time.